fix: import parser, close #61

Author: Scrum

lib/index.js

@@ -3,7 +3,7 @@
 const fs = require('fs');
 const path = require('path');
 const posthtml = require('posthtml');
-const parser = require('posthtml-parser');
+const parser = require('posthtml-parser').default;
 const {match} = require('posthtml/lib/api');
 const expressions = require('posthtml-expressions');